From the viewpoint of global warming, there are some moves to restrict the use of hydrofluorocarbon (HFC)-based refrigerants (for example, R410A, R404A, R407C, R134a, and the like) with high global warming potential as refrigerants adopted for air-conditioning apparatuses. Accordingly, air-conditioning apparatuses that adopt refrigerants with small global warming potential (for example, HFO1234yf (hydrofluoroolefin), carbon dioxide, and the like) instead of HFC-based refrigerants have been proposed (see, for example, Patent Literature 1).
When an air-conditioning apparatus is installed in a large structure such as an office building, for example, the distance between an outdoor unit and an indoor unit becomes long in some cases. As a result, the refrigerant pipe becomes long, which increases the refrigerant circuit scale (system capacity). In air-conditioning apparatuses with large refrigerant circuit scale, in comparison to those with small refrigerant circuit scale, the flow rate of refrigerant increases accordingly, which increases the pressure loss of refrigerant. Accordingly, the problem is addressed by, for example, increasing the inside diameter of a refrigerant pipe through which a low pressure refrigerant that undergoes noticeable pressure loss flows.
In addition, as a technique for reducing pressure loss, there has been proposed a technique in which a bypass is provided from a refrigerant pipe through which a high pressure liquid phase refrigerant flows (high pressure side refrigerant pipe), to a refrigerant pipe through which a low pressure refrigerant flows (low pressure side refrigerant pipe) (see, for example, Patent Literature 2). The technique disclosed in Patent Literature 2 has a refrigerant circuit configuration in which a bypass is provided from the high pressure side refrigerant pipe to the low pressure side refrigerant pipe so that a part of the high pressure liquid phase refrigerant is passed to the low pressure side refrigerant pipe. Through this configuration, of the refrigerant flowing through the low pressure side refrigerant pipe, a low pressure refrigerant that undergoes large pressure loss is reduced in flow rate, thereby reducing pressure loss.